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Question: Answered & Verified by Expert
The path difference between two interfering light waves meeting at a point on the screen is $\left(\frac{57}{2}\right) \lambda$. The band obtained at that point is
PhysicsWave OpticsMHT CETMHT CET 2021 (24 Sep Shift 2)
Options:
  • A $29^{\text {th }}$ bright band
  • B $57^{\text {th }}$ dark band
  • C $57^{\text {th }}$ bright band
  • D $29^{\text {th }}$ dark band
Solution:
1836 Upvotes Verified Answer
The correct answer is: $29^{\text {th }}$ dark band
Path difference $=\frac{57}{2} \lambda=28.5 \lambda$
Since the path difference is not an integral multiple of $\lambda$, it is not a bright bond.
Path difference for $n$th dark band is given by $\left(n-\frac{1}{2}\right) \lambda$
Hence $\mathrm{n}=29$.

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